Assert usage of client credentials for account registration (#34828)

app/controllers/api/base_controller.rb

@@ -50,6 +50,10 @@ class Api::BaseController < ApplicationController
     nil
   end
 
+  def require_client_credentials!
+    render json: { error: 'This method requires an client credentials authentication' }, status: 403 if doorkeeper_token.resource_owner_id.present?
+  end
+
   def require_authenticated_user!
     render json: { error: 'This method requires an authenticated user' }, status: 401 unless current_user
   end